Small Cabin

Small Cabin Forum
 - Forums - Register/Sign Up - Reply - Search - Statistics -

Small Cabin Forum / General Forum / Honda V-twin engines
Author Message
paulz
Member
# Posted: 3 Jan 2022 10:06 - Edited by: paulz
Reply 


I've gotten this UTV my neighbor gave me running. Got plenty of power and with 4wd I should get some use out of it. But I can't get it to idle. Has one of those common Honda GX series V-twin engines. The gas pedal connects to the governor, which connects to the carb. Right now it runs at mid rpm, drops down and the governor kicks it back up. Problem is it has a centrifugal clutch that needs to be at low rpm to shift gears.

Now here's the odd thing: the carb has no idle (pilot) circuit. No pilot jet, no mixture screw, nothing. Just the main jet and needle. It does have an idle speed screw, which will bring it up to an rpm high enough to stay running but too high to put in gear. I have checked for vacuum leaks, the throttle shaft has a bit of play but spraying WD40 at it does nothing. Ebay has carbs for $30 but they looks the same and nothing I can find wrong with this one. Might try one anyway but just thought I'd check per chance it anyone has had this issue.
20211025_1707141.j.jpg
20211025_1707141.j.jpg


Aklogcabin
Member
# Posted: 3 Jan 2022 10:35
Reply 


Does it need the air cleaner on to run correctly ? Can you disconnect the governor and run it ?
I think you're going in the right direction. The pilot controlling the lower rpm. Maybe a port hole that is metering it. Did you wash the carb down with cleaner ? In case there is dirt in a port?
Good luck

paulz
Member
# Posted: 3 Jan 2022 11:47
Reply 


Good thought but same issue with air cleaner on. Yes I can run it with the gov disconnected, operating the throttle by hand. Same thing, it will die out unless I either bring up the revs or partially cover the carb throat to richen it up. Carb is spotless inside, not the usually corrosion and gum.

I'm just confused as to why, on a vehicle that needs a low idle, there is no idle circuit, jet or mixture screw. It's more like a generator carb, where the engine just runs at a constant high rpm.

This thing, a Bush Hog, was only sold briefly and all were recalled for some reason (except this one apparently). Maybe they just used an off the shelf Honda engine of the wrong type carb. I'm going to see if I can get a cheap carb with an idle circuit. The charging system is not working either, no AC out of the stator, so that's another thing. It's probably worth $1K or better so it's worth playing around with it a little. Goes great, got a tilt bed, hydraulic brakes..

Brettny
Member
# Posted: 3 Jan 2022 11:58
Reply 


Alot of 4 stroke stuff sold in the last 15yrs dosnt have mixture screws.

I am suprised it dosnt have a idle jet or passage. Have you tried cleaning the jets out with a single strand from a copper wire? Usualy after the second shot cleaning the carb I just buy a new one, there so cheap now.

paulz
Member
# Posted: 3 Jan 2022 12:44
Reply 


There is only one jet, at the center of the float bowl. Normally there is a second smaller pilot jet next to it. I'm not at the cabin so can't take a photo. The jet is clear both visually and operationally since it's fine at higher RPM. I know some EPA carbs of late have no idle mixture screw but should still have the circuit.

Oddly, the online diagram of the carb that looks like mine does show a second jet (13) but unless I'm going blind it's not in my float area. I did read someone saying there was a screw plug in the top of the carb (not even sure it was my carb he was talking about) that has a jet under it but again I don't see that.

https://www.firedog.com/catalog/honda-engines/engine/gx/gx620/gx620-qaf1-engine-jpn-v in-gcad-1000001-to-gcad-1999999/carburetor

I'll take some photos when I go back out in a couple days. Back burner project, no rush. Thanks for the help.

Bruces
Member
# Posted: 3 Jan 2022 13:10
Reply 


How is the valve adjustment ?

paulz
Member
# Posted: 3 Jan 2022 14:02
Reply 


Good point, I need to check. This is one of those "do I really want to mess with this thing?" deals so I've been trying to dive in as little as possible.

Aklogcabin
Member
# Posted: 3 Jan 2022 14:05
Reply 


Yeppers like Bruces says. It probably has an automatic cam chain adjuster but they stick. Is there a removable plug where you can see the timing lines. Then check the value clearances.
Looks like a cool ride

toyota_mdt_tech
Member
# Posted: 3 Jan 2022 20:50 - Edited by: toyota_mdt_tech
Reply 


Paulz, I see your pilot jet, part #7

Main jet #27, pilot just, 13. Take part #7 out and look at it. In my Honda EU2000, I couldnt find the pilot jet, it was on the outside of the carb.
Symptom is plugged idle (pilot) circuit, and do noy bypass the governor.

paulz
Member
# Posted: 3 Jan 2022 21:08 - Edited by: paulz
Reply 


Here is the Ebay carb listed for these engines and looks like mine. I didn't notice that brass screw on the top right, maybe I have it. Maybe that's it, or has something to do with a pilot circuit! May head back out there tomorrow.

https://tinyurl.com/38esddf9
carby.JPG
carby.JPG


toyota_mdt_tech
Member
# Posted: 4 Jan 2022 08:30 - Edited by: toyota_mdt_tech
Reply 


Well, nice to see an ebay option. That is your pilot screw adjustment. I suspect its set probably around a turn or smidge more, remove it completely, cation, it has a spring, but may have a small flat washer and oring on the end for a nice seal. If you see the washer, it has an oring, so be warned. Small, easy to lose or overlook...if it has that set up.

Remove the pilot screw, get a can of carb or brake cleaner with red straw, blow through screw opening, should be clear through pilot jet in fuel bowl and small tiny fuel inlet just in front of the throttle blade at the bottom of carb bore. You want cleaner to squirt through all those passages with ease. I am certain its sat, fuel dried up and gummed up that teeny circuit is all.

Might add, your carb may have that screw capped too.
Ebay carb link showed fuel cut solenoid at bottom of carb, this shuts fuel off from pilot circuit with key off, make sure its energizing. (usually removing oring on end will by pass this, good for a test)

But my gut says its just plugged, solenoid could be plugged too. Energize it, listen for a nice little click.

Tim_Ohio
Member
# Posted: 4 Jan 2022 09:03
Reply 


Your crab looks like it has a fuel shutoff solenoid attached at a right angle on the bottom of the bowl. This is intended to shut fuel off simultaneously with the ignition so as not to have a backfire/after-fire occur. The valve is often the reason you here an engine increase and decrease in idle speed when it is supposed to just be idling. The valve is malfunctioning. This might be the problem and is not too expensive to replace. You might consider trying that before anything else.

Of what toyota_mdt_tech says, this is probably the cause. It is very common.

Tim_Ohio

paulz
Member
# Posted: 6 Jan 2022 16:14
Reply 


Finally back at the cabin. Had to pass a kidney stone, a rare chance to experience severe pain. My third one.

The good news is my carb does have that adjuster screw, it's hidden under some cowling when on the engine. The bad news is as soon as I tried to turn it it broke off. Seized in the carb body. Think it's time for a cheap Ebay carb.

But I still don't understand where the pilot circuit gets it fuel. Here's the float area. Only the main jet. The other hole is for the float needle.
20220106_123620.jpg
20220106_123620.jpg
20220106_123533.jpg
20220106_123533.jpg


toyota_mdt_tech
Member
# Posted: 7 Jan 2022 08:00
Reply 


I'd bet it gets it from the same source as the main. Pilot uses manifold vacuum, while main uses venturi vacuum (low pressure created as air moves through venturi (narrow point) in carb would be my guess. Manifold vacuum in front of blade pulls fuel into pilot, as throttle is opened, vacuum diminishes, then fuel goes into high speed circuit (main) would be my guess. But yes, normally see both side by side in bottom of bowl.

Lot of times you can look at carb body, see passages casting and bored with end plugs to ID a circuit.

paulz
Member
# Posted: 7 Jan 2022 10:37
Reply 


Quoting: toyota_mdt_tech
I'd bet it gets it from the same source as the main.


Must be. Another weird thing, look at the float bowl gasket. Two small holes, neither open to the carb. Straight up from those holes is where that mixture screw is. And, where is the float bowl overflow outlet? If crap gets in the float needle gas is just going to flood into the engine.

With the broken off mixture screw stuck in there I can't spray cleaner in there to see where it goes. I'll be investigating when the new carb gets here.

More to follow..

toyota_mdt_tech
Member
# Posted: 7 Jan 2022 15:42
Reply 


Paulz, I saw those holes in the gqsket, but image, didnt see matching holes in carb body, if there is holes it mates with, then I bet it DOES pick up fuel at bottom of bowl into that hole and to low speed mixture screw.

Nate R
Member
# Posted: 8 Jan 2022 08:29
Reply 


See how the screw is narrower there, where it broke? I bet that's intentional. Might be set and then loctite used to hold it in place as an anti-tampering setup. Regs are stricter on that now for emissions.

Overflow for the carb? Probably not with today's evaporative emisisons regs. That would let too many hydrocarbons float out into the air when it sits. This is a good thing, as it keeps your fuel fresh longer!

gcrank1
Member
# Posted: 8 Jan 2022 10:18
Reply 


My guess is the screw is set, and locked, in the right position. Now 'all' you have to do is get the passages to and from it cleared. Ive used lacquer thinner and brass wire. Time consuming and futzy but its easy bench work.

paulz
Member
# Posted: 8 Jan 2022 10:24
Reply 


Yeah the gas tank is lower than the carb, plus it has that solenoid, so it won't leak when it's off, and if something sticks in the needle when running it will just flood out.

Confused on that mixture screw. You can see in the photo there are no threads. Maybe that's a brass insert that is supposed to stay in the carb. I can turn the screw part but it does not move it outward. New carb due next Thursday. I should just slam it in but will probably take it apart for posterity.

toyota_mdt_tech
Member
# Posted: 10 Jan 2022 20:37
Reply 


Quoting: Nate R
See how the screw is narrower there, where it broke? I bet that's intentional



It in, that silver cap is a pressed on limiter cap and if you try to remove it, the screw will break and the break away point. Nate is right. I have a Honda walk behind mover and it did the same thing. I was able to move it out with a pocket screwdriver, ordered a new one. Never installed limiter cap.

The threaded part is still in the hold, see if you can work it out with a pocket screwdriver.

paulz
Member
# Posted: 11 Jan 2022 11:51
Reply 


Hmm, had another look, there are screw threads in the carb body, but none on the broken off piece. Maybe a third piece is missing.

Anyway new carb due Thursday.
20220111_083643.jpg
20220111_083643.jpg


gcrank1
Member
# Posted: 12 Jan 2022 09:50
Reply 


Looks like the needle tip is broken off in there
IF you have a small enough needle-nose pliers, more likely a strong tweezers, you might get it to move/pull after soaking with lacquer thinner?

paulz
Member
# Posted: 13 Jan 2022 17:07 - Edited by: paulz
Reply 


New carb arrived. Looks identical but no limiter screw. I popped the float bowl off, same thing, no pilot jet.

Back at the cabin this weekend to try it out.
20220113_1349521.j.jpg
20220113_1349521.j.jpg


Nate R
Member
# Posted: 13 Jan 2022 18:31
Reply 


The pilot jet is behind that screw. It's just not in the bowl. Should be a passage to get fuel up there.

paulz
Member
# Posted: 13 Jan 2022 18:54
Reply 


Well that's probably a good thing the way they plug up in float bowls.

paulz
Member
# Posted: 15 Jan 2022 17:22
Reply 


New carb is on, and it idles nice and slow! Oddly though, I get nothing out of that mixture screw, all the way in or out. Will play with it more but for now it's nice to put it in gear without the centrifugal clutch being engaged.

Thanks for the help.

toyota_mdt_tech
Member
# Posted: 16 Jan 2022 16:43
Reply 


Could it be a high speed screw? Where does it end up, middle of venturi (high speed) or in front of throttle blade (low speed/idle/pilot circuit)

I suppose you could look at the original to find out.

paulz
Member
# Posted: 16 Jan 2022 19:01
Reply 


I opened up the old carb again, and this time pulled out everything above the main jet (which I should have done before). There is a tube that runs through the venturi up into the top, where that mixture screw is. And a pilot jet, or orifice at the top. It's plugged.

I tried pulling the broken adjuster screw out with tweezers, won't budge, so I can't trace the whole circuit. But it indeed must be a pilot circuit.
20220116_151706.jpg
20220116_151706.jpg


toyota_mdt_tech
Member
# Posted: 16 Jan 2022 20:26
Reply 


Quoting: paulz
But it indeed must be a pilot circuit.



I think your right, high speed if there is one is almost always in bottom of bowl. Emissions, those went away years ago.

Hey, use the good alkie free stuff and does that carb have a bowl drain and a fuel shut off valve?

paulz
Member
# Posted: 16 Jan 2022 20:58
Reply 


I'm so used to motorcycle slide carbs, looking down it I assumed that tube was a needle. But of course there is no slide, lol.

It has a shut off solenoid but I clipped the needle off. The fuel tank is below the carb, there is a pump to get it there so no fuel runs out the inlet hose when it's off. The wiring on this thing is funky, if I get it sorted maybe I'll put the other solenoid back on it.

It does have a bowl drain. Now that I understand it better, the schematic makes more sense. #13 goes above 14, not next to it as I assumed. Also shows the mixture screws, 7 for the adjustable and 29 for the limiter version. Odd they don't show a point on them though.

Seems like a good idea to have the pilot jet up and out of the float bowl where they commonly plug up from dried coagulated fuel. Didn't help this one though..

https://www.cyclepartsnation.com/oemparts/a/hen/509464d2f8700230ac8c882a/carburetor-1
Screenshot_2022011.png
Screenshot_2022011.png


Your reply
Bold Style  Italic Style  Underlined Style  Thumbnail Image Link  Large Image Link  URL Link           :) ;) :-( :confused: More smilies...

» Username  » Password 
Only registered users can post here. Please enter your login/password details before posting a message, or register here first.